I think we need to rethink our model of medical education, in the sense that not all people come to med school with the same training. For example, I had a BS in biology and had already taken some classes like immunology that ended up being VERY similar to some of my 1st year medical school classes. I think it would have to be done very carefully, but I don't see why we couldn't in some way adapt 4 year med school programs so that the students could learn better. For example, if someone had years of experience as a PA or RN, they might not need the "intro to physical diagnosis" type sessions, just like I didn't really need to take a couple hours of immunology for several weeks and a test that was easier than my undergrad upper-level immunology course. Also, there might be people who would be ready for med school graduation 3-4 months early, and others who struggled more and might need an extra 5 months (instead of being failed out, etc.). This is sort of what happens with people getting PhD degrees. I would not have a problem with a PA getting some sort of advanced standing (not skipping 2-3 years of med school but I think could certainly skip the silly 1st year intro to physical exam course or "get to know seeing patients" type touchy feely stuff). I think people with MS or PhD degrees already in life sciences could potentially test out of certain subjects in 1st and maybe 2nd year, and use the time for research, or to practice seeing patients.
Normally I am a big traditionalist, but maybe we need to rethink some things, especially given the physician workforce shortage (in primary care, psych, etc.). It is really not that crazy given all the foreign medical grads we let in every year from India, etc. I'm not saying a lot of them aren't super smart and competent, but if you think about it many residency directors really don't know what these people have been taught, clinically, nor what their med school course work was like. All they have is some USMLE scores to base their judgment on.
I think PA's and NP's are not a bad thing and shouldn't necessarily be seen as a stepping stone to some other career or degree, but I'm sure some PA's could and should become excellent physicians.